I'll bite.
As I just posted in another thread - communication in relationships is one of the big pillars that they are built on. The second is boundaries. Everyone automatically assumes boundaries are sexual in nature, but in reality they encompass so much more from how you like to eat your food to what your political agenda is. If you can / can't abide by something it can affect your relationship. Ever know / see someone where there is a little annoyance that irks them about their partner and how they blow that out of proportion? Thats because there isn't an honest conversation about boundaries and abiding by them. Like how I knew a couple where one person couldn't stand how their partner chewed with their mouth open. When the partner wasn't present they'd go ON and ON about their partner's nasty habit of chewing. It was funny - but in the end the relationship didn't work out.
So it goes with having an open relationship. I've been in my fair share of relationships both long term and short term, and the big key to having an open relationship (which I've had) goes back to boundaries and communication. What do you want out of it, what do you get out of it, why are you doing it, and what limits do you have? Have that talk, and really listen and come to terms with what you discuss about having an open relationship. Like, can it only happen at home where you are considered safe? Or is that too much? It has to happen somewhere else. How many times a week / month / year is this allowed? What can you do during hookups? Is any emotional attachment allowed?
Having an open relationship can be just as healthy as a 'closed' relationship if there is an honest conversation about why you have one in the first place. I will say they take a considerable amount of work. Its not easy, and its not for those with jealousy issues. Also, the relationship you have notwithstanding being open better be a strong one. When you are open, you are going to be having sex with people who aren't your partner, or vice versa. That can effect your ego or your partner's ego. No matter how much you are prepared for it. However, it can also be rewarding. You can come to terms with your own needs / flaws and work on them with your partner. It can become a tool to dealing with your relationship and help you strengthen it.
In a previous relationship I had, it was totally one sided open. That was due to medical issues, and I was the one who was able to go outside of the relationship. The relationship broke down due to other issues than it being open. But yes, they can be one sided, or equal. Just depends on the situation.